Pen-type drug delivery devices are used for injections by persons without formal medical training. This is increasingly common for self-treatment among patients having diabetes or the like. Such self-treatment enables patients to effectively manage their disease. Pen type drug delivery devices usually comprise a housing in which a drive mechanism is located. Some kinds of drug delivery devices also comprise a compartment to accommodate a cartridge in which the drug is contained. By means of the drive mechanism, a piston in the cartridge is displaced such that the drug accommodated therein is dispensed through a needle.
Prior to injection, the required dose of a drug is set by means of a dose setting mechanism. Common designs of dose setting mechanisms comprise a number of tubular or sleeve-like elements such as a dose dial sleeve, a dose indicating sleeve, a drive sleeve or a ratchet sleeve. Such sleeves are often accommodated within and connected to each other.
Some devices may be reused when a full amount of medication has been delivered from the drug delivery device.